There are many kinds of implantable medical devices. Some monitor patient conditions while others disperse some form of therapy. One particular type of implantable medical device is an implantable cardiac therapy device, or ICTD. ICTDs are implanted within the body of a patient to monitor, regulate, and/or correct heart activity. ICTDs include implantable cardiac stimulation devices (e.g., implantable cardiac pacemakers, implantable defibrillators) that apply stimulation therapy to the heart as well as implantable cardiac monitors that monitor heart activity.
With advances in microelectronics, many implantable medical devices are miniature computers with memory and processing capabilities. Such devices are capable of being programmed remotely by an external programming device, often called a “programmer”. An implanted device and a programmer communicate using wireless telemetry technologies. Early telemetry systems were passive, meaning that communication was unidirectional from the programmer to the implanted device. Passive telemetry allowed a treating physician to download instructions to the implanted device following implantation. Due to power and size constraints, early commercial versions of implanted devices were incapable of transmitting information back to the programmer.
As power capabilities improved, active telemetry became feasible. This allowed bi-directional communication between the implanted device and the programmer. With active telemetry, the treating physician is able to both program the implanted device and retrieve information from the implanted device to evaluate heart activity and device performance.
Current telemetry systems have limited communication range between the programmer wand and device. The programmer utilizes an electromagnetic wand that is placed within a few inches of the implanted cardiac device to communicate with the implanted device. The wand contains a coil that forms a transformer coupling with the telemetry circuitry in the device and low frequency signals are transmitted via the coupling. Due to the limited range, such telemetry systems are often referred to as “short-range telemetry” or “wand telemetry”.
With advancements being made in telemetry technologies, the communication range is expected to increase beyond a few inches to several feet or more. An increased telemetry range will provide many advantages, including more mobility for the patient during telemetry and more flexibility in the positioning of the telemetry antenna. For example, increasing the range would allow a programmer to monitor, for example, a patient exercising on a treadmill, or moving around at home, or a patient that walks into a waiting room.
Unfortunately, an increased telemetry range does not come free of problems. One new problem introduced by longer-range telemetry is the potential of interference between separate programmers that are being used to program multiple devices within a common telemetry range. Traditionally, telemetry systems have employed a single communication channel, which enables a single programmer to communicate with a single implantable device. This was a reasonable approach given that the communication range was limited to a few inches. But, as the range increases, there is the potential for interference on that channel. This interference may be in either or both directions of the telemetry link between the programmer and the implantable device.
Accordingly, there is a need for a more comprehensive telemetry architecture that accommodates multiple programmers communicating with multiple implantable devices within a common communication range.